Graylog 4.0 Sharing stream not working

Hi,

I updrade today from Graylog 3.3… to 4.0 everything is working except the new sharing feature.
Every time I try to share a stream or Dashboard I get only an error message:

–snipp–
Preparing shares for All events “stream” faild woth status: IOException encountered while reading from a byte array input stream - cannot POST https:/…/api/authz/shares/entities/grn::::stream …
–snapp–

The installation is on Debian 10 with the graylog apt repository.

Has somebody an idea what I can do to fix this?

Regards, Dirk